Spring Boot CLI - Hello World Example

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In this example, we'll create a Spring Boot + MVC + Rest based Web application.

Step 1: Create source Folder

Create a folder FirstApplication in E:\Test folder.

Step 2: Create Source File

Create FirstApplication.groovy file in E:\Test folder with following source code −

@RestController
class FirstApplication {
   @RequestMapping("/")
   
   String welcome() {
      "Welcome to Howcodex.Com"
   }
}

Step 3: Run the application

Type the following command −

E:/Test/> spring run FirstApplication.groovy

Now Spring Boot CLI will come into action, download required dependencies, run the embedded tomcat, deploy the application and start it. You can see the following output on console −

Resolving dependencies..........................................................
................................................................................
........................

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _> | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v1.5.8.RELEASE)

2017-11-07 17:36:55.703  INFO 5528 --- [       runner-0] o.s.boot.SpringApplication: 
Starting application on ...
2017-11-07 17:36:55.707  INFO 5528 --- [       runner-0] o.s.boot.SpringApplication: 
No active profile set, falling back to default profiles: default
2017-11-07 17:36:56.067  INFO 5528 --- [       runner-0] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@4c108392: startup date [Tue Nov 07 17:36:
56 IST 2017]; root of context hierarchy
2017-11-07 17:36:57.327  INFO 5528 --- [       runner-0] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2017-11-07 17:36:57.346  INFO 5528 --- [       runner-0] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2017-11-07 17:36:57.354  INFO 5528 --- [       runner-0] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.23
2017-11-07 17:36:57.537  INFO 5528 --- [ost-startStop-1] org.apache.catalina.loader.WebappLoader  : Unknown loader org.springframework.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader@41bfad4f class org.springframew
ork.boot.cli.compiler.ExtendedGroovyClassLoader$DefaultScopeParentClassLoader
2017-11-07 17:36:57.567  INFO 5528 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-11-07 17:36:57.567  INFO 5528 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1500 ms
2017-11-07 17:36:57.725  INFO 5528 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2017-11-07 17:36:57.730  INFO 5528 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-11-07 17:36:57.730  INFO 5528 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-11-07 17:36:57.730  INFO 5528 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-11-07 17:36:57.730  INFO 5528 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2017-11-07 17:36:58.012  INFO 5528 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@4c108392: startup date [Tue Nov 07 17:36:56 IST 2017]; root of context hierarchy
2017-11-07 17:36:58.066  INFO 5528 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto public java.lang.String FirstApplication.home()
2017-11-07 17:36:58.070  INFO 5528 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2017-11-07 17:36:58.071  INFO 5528 --- [       runner-0] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web
.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2017-11-07 17:36:58.096  INFO 5528 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-11-07 17:36:58.096  INFO 5528 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-11-07 17:36:58.129  INFO 5528 --- [       runner-0] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-11-07 17:36:58.626  INFO 5528 --- [       runner-0] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2017-11-07 17:36:58.696  INFO 5528 --- [       runner-0] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2017-11-07 17:36:58.699  INFO 5528 --- [       runner-0] o.s.boot.SpringApplication               : Started application in 3.529 seconds (JVM running for 190.196)
2017-11-07 17:37:20.217  INFO 5528 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2017-11-07 17:37:20.218  INFO 5528 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started

2017-11-07 17:37:20.238  INFO 5528 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 20 ms

Step 4: Browse the application in Browser

Our spring based rest application is now ready. Open url as "http://localhost:8080/" and you will see the following output −

Hello World

Important points

Consider the following points to understand how Spring CLI works.−

  • All dependency JARs are downloaded for the first time only.

  • Spring CLI automatically detects which dependency JARs are to be downloaded based on the classes and annotations used in code.

  • Finally after the compilation of the code, deploy the war file on an embedded tomcat and start embedded tomcat server on the default port 8080.

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